The present inventions relate generally to electric motors, and more particularly, to an electric motor with a rotor made of a series of laminations.
An example of a conventional rotor 10 for an electric motor is shown in FIG. 1. As shown, the rotor 10 may be made of a series of laminations 12 that are stacked together. In the particular rotor 10 shown in FIG. 1, the poles 14 of the rotor 10 are formed by magnetically permeable segments 16 that are isolated from each other by insulated regions 18 disposed between the segments 16. Thus, the rotor stack 20 of FIG. 1 may be considered a reluctance rotor 10 for a reluctance electric motor. In many embodiments, the insulated regions 18 are air spaces 18, or voids 18. Although not shown, a rotor shaft is disposed through the center hole 21 of the stack 20.
In order to maintain the physical integrity of the rotor stack 20 and prevent the laminations 12 from rotating relative to each other, a mechanical structure is required to keep the segments 16 of adjacent laminations 12 aligned with each other. One common solution to satisfy this need is illustrated in FIG. 1. As shown, each of the segments 16 of the individual laminations 12 are interconnected with each other with an interconnection 22, which is sometimes referred to as a bridge 22. The interconnection 22 is typically an integral thin portion of the lamination 12 that extends between and connects adjacent segments 16 together. Thus, as shown in FIG. 1, each of the laminations 12 are individually fully self-supporting. In general, most or all of the laminations 12 in the stack 20 have matching shapes.
In order to hold the stack 20 of laminations 12 together in a rigid structure, some type of additional hardware is typically needed to secure the laminations 12 together. One type of conventional securing hardware is shown in FIG. 1. As shown, one or more pins 24 located off-center from the rotor shaft may extend through a hole 26 in the laminations 12. Thus, the pins 24 maintain the laminations 12 in lateral alignment with each other and prevent the laminations 12 from rotating relative to each other. The pins 24 may also be used to squeeze the laminations 12 against each other. For example, end plates 28 may be provided at opposite ends of the stack 20, and the pins 24 may also extend through the end plates 28. The pins 24 may then be used to engage the end plates 28 (e.g., with threaded fasteners) to squeeze the end plates 28 and the laminations 12 together.
Although the above-described arrangement is widely used to form electric motor rotors, the design results in less than optimal performance in electric motors. As shown in FIG. 2, when the rotor 10 is used in an electric motor, magnetic flux is generated by the stator and directed at the rotor 10. During use of the electric motor, the magnetic flux is cycled and rotated around the stator in order to attract and/or repel the rotor poles 14 to force the rotor 10 and rotor shaft to rotate. An example of magnetic flux lines 30 directed at the rotor 10 is illustrated in FIG. 2. As shown, some 32 of the magnetic flux 30 travels through the interconnections 22 between adjacent segments 16. This portion of the magnetic flux 30 is known as flux leakage 32, since in an optimal design the magnetic flux 30 would only travel through defined rotor poles 14 and would not travel between adjacent rotor poles 14. However, in the conventional rotor 10 shown in FIGS. 1 and 2, it is difficult to prevent flux leakage 32 since the mechanical interconnections 22 between adjacent segments 16 are commonly made out of the same magnetically permeable material as the segments 16 themselves.